Service providers have been increasingly providing their web services (e.g., web sites) at third party data centers in the cloud by running a plurality of virtual machines (VMs) on a host/server at the data center. Here, a VM is a software implementation of a physical machine (i.e. a computer) that executes programs to emulate an existing computing environment such as an operating system (OS). The VM runs on top of a hypervisor, which creates and runs one or more VMs on the host. The hypervisor presents each VM with a virtual operating platform and manages the execution of each VM on the host. By enabling multiple VMs having different operating systems to share the same host machine, the hypervisor leads to more efficient use of computing resources, both in terms of energy consumption and cost effectiveness, especially in a cloud computing environment.
Non-volatile memory express, also known as NVMe or NVM Express, is a specification that allows a solid-state drive (SSD) to make effective use of a high-speed Peripheral Component Interconnect Express (PCIe) bus attached to a computing device or host. Here the PCIe bus is a high-speed serial computer expansion bus designed to support hardware I/O virtualization and to enable maximum system bus throughput, low I/O pin count and small physical footprint for bus devices. NVMe typically operates on a non-volatile memory controller of the host, which manages the data stored on the non-volatile memory (e.g., SSD, SRAM, flash, HDD, etc.) and communicates with the host. Such an NVMe controller provides a command set and feature set for PCIe-based SSD access with the goals of increased and efficient performance and interoperability on a broad range of enterprise and client systems. The main benefits of using an NVMe controller to access PCIe-based SSDs are reduced latency, increased Input/Output (I/O) operations per second (IOPS) and lower power consumption, in comparison to Serial Attached SCSI (SAS)-based or Serial ATA (SATA)-based SSDs through the streamlining of the I/O stack.
Currently, a VM running on the host can access a plurality of storage devices (e.g., PCIe-based SSDs) locally coupled to the physical NVMe controller attached to the host. Here, the number of storage volumes the VM can access is constrained by the physical limitation on the maximum number of physical storage units/volumes that can be locally coupled to the physical NVMe controller. Since the VMs running on the host at the data center may belong to different web service providers and each of the VMs may have its own storage needs that may change in real time during operation and are thus unknown to the host, it is impossible to predict and allocate a fixed amount of storage volumes ahead of time for all the VMs running on the host that will meet their storage needs. Enabling access to remote storage devices over a network can provide extensible/flexible storage volumes to the VMs during a storage operation.
When the VM is migrated (either live or regular/quiesced) from the current host (the source host) it is running on to another host (the destination host) without causing any interruption to the users or applications served by the VM, all resources (e.g., data, storage, network connections, etc.) currently used by the VM need to be transferred/copied from the source machine to the destination machine. Since the VM may have pending storage operations to the remote (not just local) storage devices via the NVMe controller, it is important to be able to handle such pending storage operations via the NVMe controller properly during the migration of the VM.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent upon a reading of the specification and a study of the drawings.